40 Mr. W. King; on certain Genera 



D 



valvulars, the imperforate valve affords attachment to other two 

 muscles which pass upwards from the crural base (where each one 

 is divided), and become inserted in the upper part of the pedicle : 

 it is proposed to name these the inferior pedicle muscles. With 

 one exception, the foregoing description agrees with that given 

 by Professor Owen in his memoir a . On the Anatomy of the 

 Brachiopoda*," in which it is stated, that the muscles which have 

 been termed the valvulars pass into the upper part of the pedicle, 

 — a statement which I am led to suspect may have arisen simply 

 from the superior termination of these muscles in the specimens 

 examined by this distinguished anatomist having been so close to 

 the upper part of the pedicle as to appear as if attached to it. 



Productus, &c. 



An examination of a number of Palliobranchiate fossils has con- 

 vinced me that a muscular system similar to that of Terebratula 

 dorsata characterized the genera Productus, Lepttena, Strophomena, 

 Orthis, Spirifer and Chonetes. In the deltidial or corresponding 

 valve of these shells, there are impressions answering to the six 

 muscles which have been described as passing from the same 

 valve of Terebratula dorsata ; and in the opposite valve there are 

 impressions corresponding to the four terminal divisions of the 

 valvulars, and the hinge is generally furnished with a prominency 

 which has clearly served as a fulcrum for the cardinals f. It is 

 necessary to mention that it is only in certain species of these 

 genera that the muscular impressions can be made out ; in general 

 they are confluent, in which case it is difficult to define them J. 

 I have not yet seen any positive indication of impressions in 

 these fossils answering to the two muscles passing from the cru- 

 ral base to the upper part of the pedicle : I am strongly disposed 

 however to think that this does not arise from the absence of 

 such muscles, but rather from their not having produced impres- 

 sions strong enough to remain visible — a supposition that cannot 

 be objected to, considering how very faint the impressions of the 

 inferior pedicle muscles are in Terebratula §. 



* Transactions of the Zoological Society of London, vol. i. p. 151. 



f Those fossils which have no cardinal prominency, as certain Orthises, 

 Spirifers, &c, have nevertheless impressions in the centre of the hinge, 

 which clearly show that the cardinal muscles were neither abrogated nor 

 implanted elsewhere. Hypothyris pslttacea serves as an exceptional case 

 in another genus. 



% In a " Monograph of the Invertebrate Fossils of the Magnesian Lime- 

 stone of the County of Durham," which I am preparing for publication, a 

 more detailed account will be given of the muscular system, &c. of most of the 

 genera mentioned in the text, together with numerous illustrative figures. 



§ In Orthis Michelini the inferior pedicle muscles appear to have been 

 attached to the socket-walls or socket-plates, as their surface displays marks 

 of muscular attachment. 



